In the manufacture of cushioning structures of elastomeric foam, a syrup or compounded latex comprising the elastomeric-foam progenitors is cured in a mold under conditions which result in "blowing" and curing. Subsequent cutting into the various shapes and sizes required results in the formation of scrap, i.e., pieces too small to have utility per se. It is known to recover such scrap by shredding, wetting with a fluid curable to an elastomeric binder, and remolding the mass under conditions to cure the binder to yield a unitary foam structure which has useful properties, albeit somewhat different from those of the original foam.
Typical of the prior art are U.S. Pat. Nos. 3,114,722, 3,300,421 and 3,401,128. Essentially these describe coating comminuted polyurethane foam particles with a bonding agent comprising a prepolymer of polyurethane -- the reaction product of a polyhydroxy compound with a polyisocyanate -- and hastening the bonding process by placing the shredded polyurethane foam and prepolymer in a mold, wherein the prepolymer forms a coating around the particles of shredded material, applying heat and pressure, and recovering a molded article. Such a product is commonly referred to as a "rebonded" structure. It is improved in load-support characteristics over the original, which the cushioning trade regards as a substantial advantage; but it is somewhat higher in density than the original foam from which the shreds were obtained. This is a disadvantage. It still resembles the original (e.g., polyurethane) foam, however, in that although capable of bearing a somewhat greater load at a given degree of compression, it will, nonetheless, "bottom out" with moderate further loading, thus losing its cushioning characteristics.
Cushioning structures are also prepared from very low density cellular fibers which have excellent pneumatic properties. In general, these so-called pneumacel fibers are made from synthetic organic polymers and are composed predominately of small, polyhedral-shaped, closed cells, the cells being defined by thin, film-like walls of polymer. Gases contained within the cells contribute to the stiffness and pneumatic behavior of the cellular fibers. Such fibers have densities of 0.01 g./cc. or less and, due to their pressurized, pneumatic character, are noncompliant, "springy" structures. If held under compression, pneumacel will lose part of its trapped gas, but when the pressure is released it will reabsorb air and reinflate to its original size.
These fibers, in batt form, are useful as cushioning layers in mattresses, auto upholstery, or upholstered furniture for thermal insulation, or for carpet cushion underlays. Such batts are formed typically by depositing the fibers as a loose uniform batt on a continuous belt, impregnating them with a thermoplastic binder in the form of a latex, drying, heating to activate the binder, compression, and cooling before release from compression to set the batt in its compressed form. Other additives such as fire-retardants, dyes, etc. may also be applied to the batting. Some of the numerous patents on this general subject are U.S. Pat. Nos. 3,375,211; 3,375,212; 3,503,907; 3,485,711; 3,535,181; 3,743,694; 3,717,904 and 3,730,916.
Suitable pneumacel fibers are prepared from synthetic crystallizable, organic polymers, and as described in U.S. Pat No. 3,227,664, include polyhydrocarbons such as linear polyethylene, stereoregular polypropylene or polystyrene; polyethers such as polyformaldehyde; vinyl polymers such as poly(vinylidene fluoride); polyamides, both aliphatic and aromatic, such as poly(hexamethylene adipamide) and poly(metaphenylene adipamide) and poly(metaphenylene isophthalamide); polyurethanes, both aliphatic and aromatic, such as the polymer from ethylene bischloroformate and ethylene diamine; polyesters such as poly(hydroxypivalic acid) and poly(ethylene terephthalate); copolymers such as poly(ethylene terephthalate isophthalate), and the like. The polymers are of at least film-forming molecular weight. Preferably, the pneumacel fibers are made of poly(ethylene terephthalate), inflated with Freon.
The processing of pneumacel batting, manufactured as described above, into cushioning structures of the desired shapes and sizes usually requires trimming off edges, corners and the like, which trimmings are hereafter referred to as scrap pneumacel batting.